1. Field of the Invention
The present invention generally relates to a wiring structure. More specifically, the present invention relates to a wiring structure that is mainly used inside semiconductor electric power modules.
2. Background Information
A conventional power module typically has a metal base plate with an insulation plate overlying the metal base plate and internal wiring overlying the insulation plate. The metal base plate serves as a base plate for the module, and is often made of a copper plate of approximately four millimeters in thickness. The insulation plate is normally made of ceramic, and is connected to the metal base plate with solder.
The internal wiring is electrically connected to a pair of electrodes such as a collector electrode and an emitter electrode. The electrodes are often made of a copper plate of approximately one millimeter in thickness. One end of each electrode is exposed on the outside of the module and has a threaded hole so that it can be screw-connected to an external bus bar. The other ends of the electrodes are connected to the internal wiring that is arranged on the insulation plate. The internal wiring includes an emitter conductor and a collector conductor, which are often made of copper foils that are formed so as to be closely adhered to the insulation plate. Thus, the emitter conductor is electrically connected to the emitter electrode, and the collector conductor is electrically connected to the collector electrode.
A semiconductor chip is soldered onto the collector conductor. Thus, the undersurface of the semiconductor chip has the collector conductor formed thereon. Meanwhile, an aluminum wire is electrically connected between an emitter pad on a top portion of the semiconductor chip and the emitter conductor.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved wiring structure. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
It has been discovered that with the structure just described, the wiring inductance is large because the electrodes (collector electrode and emitter electrode) are separated by some distance. In addition, induced voltages limit the drive conditions of the device during high-speed switching. Also, electromagnetic waves are generated from the electrodes and cause electromagnetic interference (EMI) in the surrounding drive circuitry by frequent switching. The tendency for this problem to occur is particularly strong in intelligent power modules (IPM), in which the drive circuits are integrated inside the module. To avoid this problem, such modules are generally provided with a shielding plate in the vicinity of the drive circuitry.
However, the use of shielding plates and the like does not address the root cause of the problem. The present invention was conceived in order to solve this problem and seeks to provide a semiconductor power module or a wiring structure that uses the same wiring materials as conventional structures, while reduces the wiring inductance of the power wiring in a semiconductor power module and prevents as much as possible the emission of interference causing electromagnetic waves.
In order to achieve the aforementioned object, the wiring structure of the present invention comprises a conductive base layer, an insulation layer, a first electrical conductor and a second electrical conductor. The conductive base layer has a first main surface. The insulation layer has a first side surface facing the first main surface of the conductive base layer. The first electrical conductor faces a second side surface of the insulation layer and is configured with a first current flowing direction. The second electrical conductor is configured with a second current flowing direction that is opposite to the first current flowing direction of the first electrical conductor. The second electrical conductor overlies the first electrical conductor such opposite longitudinal edges of the second electrical conductor extend beyond corresponding longitudinal edges of the first electrical conductor at all locations by predetermined distances.
These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.